1. Field of the Invention
This invention relates to an apparatus which can simply and stably control the intensity distribution of an applied light as a desired intensity distribution and which can be applied, for example, to an apparatus for treating the cornea of an eye to be examined.
2. Related Background Art
In recent years, in the corneal refraction correcting operations, it has been practice to apply a laser beam such a as an excimer laser to the cornea of an eye to be examined to thereby incise radially the surface of the marginal portion of the cornea and adjust the curvature of the central portion of the cornea. In such laser cornea treating apparatus, the laser beam is made into a linear beam by the use of a cylindrical lens or the like and the linear beam is applied to the cornea surface of the eye to be examined, thereby accomplishing a cornea incision operation.
However, in the above-described apparatus, when incising the surface of the marginal portion of the cornea, it is difficult to incise each portion of the cornea to a desired depth because neither is the illumination distribution of the linear laser beam uniform nor is the thickness of the cornea of the eye to be examined uniform.
In the prior art, to freely control the distribution of the applied quantity of light on the irradiated surface by a light beam emitted from a light source, several kinds of filters having various density distributions must be prepared and the intensity distribution must be adjusted. Filters having such density distributions are generally made by metal deposition or optical etching or the like, but such methods of making filters are considerably complex and take much time and are inaccurate in density distribution, and it is often the case that a desired light-quantity distribution is not obtained even if a light beam is passed through the filters.
Also, where a powerful pulse laser such as an excimer laser is applied, for example, to a cornea shaping operation or the like, if the density distributions of the filters are inaccurate, no precise light-quantity distribution is obtained and further, the filters may possibly be destroyed, that is, the filters lack in durability and it is not only difficult but also dangerous to use such filters in the cornea shaping which requires precise control of a laser beam.
In U.S. Pat. No. 4,665,913, it is disclosed to scan a spot light beam on the cornea of an eye to be examined to thereby obtain a desired intensity distribution. However, the light scanning requires a varying amount of time, and this leads to the necessity of a cumbersome operation of temporarily stopping the application of the laser beam when the eye to be examined has moved and again applying the laser beam after alignment.